JP2004282290A - Clock synchronization signal transmission system, data transmission system, and method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable a receiver side to easily receive a clock of frequency equivalent to the base rate of optical time-division multiplex. <P>SOLUTION: An optical transmitter 10 makes the pulse amplitude of ch1 smaller than the pulse amplitudes of other ch2-ch4, and outputs it to an optical transmission path 12. In an optical receiver 14, the photodiode 46 of a clock reproducing apparatus 44 converts an optical time-division multiplex signal light to be inputted from the optical transmission path 12 into an electric signal. A PLL circuit 50 reproduces a clock synchronization signal of a frequency equivalent to a base rate (B) from an output of the photodiode 46. A mode lock laser 60 performs pulse laser oscillation at a frequency equivalent to the base rate (B) so as to synchronize with the reproduced clock synchronization signal. An optical separating device 66 separates an OTDM signal light from an optical path to each channel, according to a control pulse to be outputted from the laser 60. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a clock synchronization signal transmission system for transmitting a clock synchronization signal in optical time division multiplexing (OTDM) transmission, a data transmission system capable of transmitting a clock synchronization signal and channel attribute information, and a method thereof.
[0002]
[Prior art]
In an optical fiber transmission system, a bit rate of 160 Gb / s or more is being realized at a single wavelength. However, since the response speed of the electric receiver is at most 50 to 60 GHz, even if an optical pulse signal of 160 Gb / s or more is directly received, clock extraction for establishing synchronization is impossible.
[0003]
Therefore, an optical circuit for extracting a clock has been devised. For example, a method of realizing a phase locked loop (PLL) by making an ultra-high-speed optical gate circuit function as an optical pulse phase shifter, a two-stage cascade connection of an electro-absorption modulator (EA modulator) used as an optical gate modulator Method for down-converting an optical pulse signal to a low bit rate by a separating device having the above configuration, and then extracting a clock by a PLL at an electric signal stage, and an optical clock by injection locking to a mode-locked semiconductor laser or a self-excited oscillation semiconductor laser A method for playing back music has been studied.
[0004]
An apparatus and a method for extracting a clock component from an optical pulse signal to reproduce an optical clock are described in JP-A-2002-353901. By using an electric resonator having a resonance frequency of 1 / n of the clock frequency of the input optical pulse signal and a semiconductor mode-locked laser driven by its output, a frequency of 1 / n of the clock frequency of the input optical pulse signal is obtained. Is described.
[0005]
Japanese Patent Application Laid-Open No. 10-173634 describes a configuration in which a low-frequency signal having a frequency unique to each channel is superimposed on an optical signal of each channel by weak intensity modulation in optical time division multiplex transmission. The receiving side detects the low frequency signal and identifies the channel.
[0006]
[Problems to be solved by the invention]
Ultra-high-speed optical gates and multi-stage optical gates for clock extraction have complicated configurations and are not economical.
[0007]
In the OTDM transmission system, there is no method for efficiently transmitting attribute information (channel identification information, transfer information or routing information, network management information (notification of failure occurrence, etc.)) of each multiplexed channel. Such attribute information includes, for example, channel identification information, transfer information (routing information), and network management information. The network management information includes a failure notification. For such attribute information, there has been no other method than the conventional method in which an optical carrier is pulse-modulated and transmitted like the main information data. Therefore, in the receiving device and the router, there is no other way but to convert both the data signal and the attribute information into an electric signal and then demodulate the electric signal with an existing electric processing system.
[0008]
A method of transmitting a monitoring signal for monitoring an optical transmission path, a control signal for controlling an optical repeater on the optical transmission path, and a response signal by amplitude-modulating a pulse signal is well known.
[0009]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a clock synchronization signal transmission system and method capable of solving such inconvenience, transmitting a clock synchronization signal efficiently, and easily extracting the clock synchronization signal.
[0010]
Another object of the present invention is to present a data system and a method for transmitting attribute information of each channel with a simple configuration.
[0011]
[Means for Solving the Problems]
A clock synchronization signal transmission system according to the present invention transmits a clock synchronization signal in an optical transmission system in which pulse signal light of n (integer) channels at a base rate (B) is time-division multiplexed and transmitted through an optical transmission path. In the system, the pulse amplitudes of k (k is equal to or greater than 1 and less than n) channel light signals of the n channel pulse signal lights before optical time division multiplexing are defined as pulse amplitudes of the remaining channels. An amplitude adjusting device that adjusts to a relatively different level, a photoelectric converter that converts the time-division multiplexed signal light transmitted through the optical transmission line into an electric signal, and a base rate (B) according to an output of the photoelectric converter. And a clock generation circuit that generates a clock synchronization signal having a frequency corresponding to an integer multiple of the frequency and determined by the k channel whose level is adjusted by the amplitude adjustment device. And wherein the door.
[0012]
With such a configuration, a clock synchronization signal having a frequency corresponding to the base rate (B) or a frequency that is an integral multiple of the frequency corresponding to the base rate (B) can be received without dividing the frequency of the clock having the frequency corresponding to the OTDM bit rate. Can be easily played. When adjusting the level of only one channel, a clock synchronization signal having a frequency corresponding to the base rate (B) can be reproduced.
[0013]
Preferably, the amplitude adjusting device includes n variable level adjusters capable of adjusting the level of the signal light of each channel, and a control device for controlling the n variable level adjusters. Thereby, the channel for adjusting the level can be selected.
[0014]
A data transmission system according to the present invention includes a pulse signal light generating device that generates pulse signal light of n (integer) channels at a base rate (B) that carries data, and an output from the pulse signal light generating device. an amplitude adjustment device that adjusts the pulse amplitude of a predetermined one-channel pulse signal light of the n-channel pulse signal light to a level relatively different from the pulse amplitudes of the other pulse signals; A multiplexer for time-division multiplexing the signal light of each channel output from the device and outputting an OTDM signal light, an optical transmission line for transmitting the OTDM signal light output from the multiplexer, and an input from the optical transmission line A splitter for dividing the OTDM signal light into two, and a clock for reproducing a clock synchronization signal having a frequency corresponding to the base rate (B) from one output signal light of the splitter. A reproducing apparatus, comprising: a photoelectric converter for converting one output signal light of the splitter into an electric signal; and a clock synchronization signal having a frequency corresponding to the base rate (B) according to an output of the photoelectric converter. A clock recovery circuit having a clock generation circuit for generating a clock signal; and a plurality of output ports, and according to a clock synchronization signal recovered by the clock recovery device, the other output signal light of the duplexer is used as a signal of each channel. A light separation device for separating the light into light and outputting the signal light of each channel from a different output port.
[0015]
With such a configuration, the optical receiver can reproduce a base-rate clock synchronization signal with a simple configuration without reproducing a clock having a frequency corresponding to the OTDM bit rate and then dividing the frequency.
[0016]
Preferably, the amplitude adjusting device includes n variable level adjusters capable of adjusting the pulse amplitude of the signal light of each channel, and a control device for controlling the n variable level adjusters. Thereby, the channel for adjusting the pulse amplitude can be selected.
[0017]
Preferably, the control device varies the level adjustment amounts of the n variable level adjusters according to the attribute information of each channel. Thereby, the attribute information of each channel can be transmitted without restricting the data transmission of each channel and the band.
[0018]
The attribute information is, for example, channel identification information, transfer information, network management information, and the like.
[0019]
Preferably, the data transmission system according to the present invention further comprises: an identification device for identifying whether the pulse signal light output from a predetermined output port of the optical separation device is the signal light of the predetermined channel; A phase adjuster that adjusts the phase of a clock synchronization signal supplied from the clock recovery device to the optical demultiplexing device according to the identification result of the device. Thereby, it is possible to control so that the pulse signal light of the predetermined channel is output from the predetermined output port of the optical separation device. By changing the predetermined channel to be adjusted to a different level, the channel output from each output port of the optical separation device can be changed.
[0020]
Preferably, the amplitude adjusting device includes n variable level adjusters capable of adjusting the level of signal light of each channel, and variable level adjusting according to a tone signal having a different frequency for each channel carrying attribute information of each channel. And a control device for controlling the level adjustment amount of the vessel. Thereby, channel identification becomes easy, and attribute information other than channel identification can be transmitted at the same time.
[0021]
For example, the pulse signal light generation device includes a pulse light source that generates a light pulse having a frequency corresponding to the base rate (B), a demultiplexer that divides output light of the pulse light source into n light beams, And n data modulators for modulating each output of the modulator according to transmission data.
[0022]
A clock synchronization signal transmission method according to the present invention is a method of transmitting a clock synchronization signal in an optical transmission system that transmits a time-division multiplexed pulse signal of n (integer) channels at a base rate (B) and transmits the optical transmission path. And adjusts the pulse amplitude of the signal light of k (k is 1 or more and less than n) of the pulse signal light of the n channels to a level relatively different from the pulse amplitude of the remaining channels. Then, the optical transmission line is transmitted, the time-division multiplexed signal light transmitted through the optical transmission line is converted into an electric signal, and a frequency corresponding to an integral multiple of the base rate (B) according to the electric signal. Then, a clock synchronization signal having a frequency determined by the k channel whose amplitude has been adjusted before transmission is generated by a PLL circuit.
[0023]
With such a configuration, the optical receiving apparatus can reproduce a clock having a frequency corresponding to the OTDM bit rate and then divide the frequency without reproducing the clock. Clock synchronization signal can be reproduced.
[0024]
In the data transmission method according to the present invention, a pulse signal light generating device generates pulse signal light of n (integer) channels of a base rate (B) for carrying data, and the amplitude adjusting device generates the pulse signal light. The pulse amplitude of the pulse signal light of one predetermined channel out of the pulse signal lights of n channels output from the device is adjusted to a level relatively different from the pulse amplitudes of the other pulse signals, and the amplitude is adjusted. The signal light of each channel output from the adjusting device is time-division multiplexed, the obtained OTDM signal light is output to an optical transmission line, and the OTDM signal light input from the optical transmission line is divided into two by a demultiplexer. The output signal light of one of the splitters is converted into an electric signal, and a PLL circuit generates a clock synchronization signal having a frequency corresponding to the base rate (B) according to the electric signal. According to the clock synchronization signal, characterized in that the other output signal light of the splitter by an optical separator for separating the signal light of each channel.
[0025]
With such a configuration, the optical receiving apparatus reproduces the clock synchronization signal having the frequency corresponding to the base rate with a simple configuration without reproducing the clock having the frequency corresponding to the OTDM bit rate and then dividing the frequency. This makes it easier to separate the OTDM optical signal into individual channels.
[0026]
Preferably, when adjusting the pulse amplitude of the pulse signal light of one predetermined channel to a level relatively different from the pulse amplitude of another pulse signal, the signal light of each channel is adjusted according to the attribute information of each channel. Is varied. Thereby, the attribute information of each channel can be superimposed on the data and transmitted without restricting the data transmission and the band of each channel.
[0027]
Preferably, the pulse amplitude of the signal light of each channel is varied according to a tone signal having a different frequency for each channel carrying attribute information of each channel. This facilitates identification of each channel.
[0028]
The attribute information is, for example, one of channel identification information, transfer information, and network management information.
[0029]
Further, it is determined whether or not the pulse signal light output from a predetermined output port of the optical separation device is the signal light of the predetermined channel, and the clock synchronization supplied to the optical separation device is determined according to the identification result. Adjust the signal phase. Thereby, it is possible to control so that the pulse signal light of the predetermined channel is output from the predetermined output port of the optical separation device. By changing the predetermined channel to be adjusted to a different level, the channel output from each output port of the optical separation device can be changed.
[0030]
【Example】
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0031]
FIG. 1 shows a schematic welfare block diagram of one embodiment of the present invention. The system according to the present embodiment includes an optical transmission device 10, an optical transmission line 12, and an optical reception device 14. In the present embodiment, the optical transmission device 10 time-division multiplexes 40 Gb / s optical signals into four channels, and outputs the signals to the optical transmission line 12. Therefore, an optical signal of 160 Gb / s propagates through the optical transmission line 12. The present invention can be applied to a wavelength division multiplexing system by adopting the configuration of the optical transmitting device 10 and the optical receiving device 14 shown in FIG. 1 for each wavelength of the wavelength division multiplexing transmission system.
[0032]
The configuration and operation of the optical transmission device 10 will be described. The pulse light source 20 outputs an optical pulse train having a single wavelength λs and a base rate (basic repetition frequency) B. Here, the base rate B is 40 GHz. The optical demultiplexer 22 divides the output pulse of the pulse light source 20 into four and supplies the four to the data modulators 24-1 to 24-4.
The data modulator 24-1 binary-modulates the amplitude of the optical pulse train from the optical demultiplexer 22 according to the data D1. Similarly, the data modulators 24-2 to 24-4 binary-modulate the amplitude of the optical pulse train from the optical demultiplexer 22 according to the data D2 to D4, respectively.
As a result, the data modulators 24-1 to 24-4 output 40 Gb / s optical pulse signals that carry the data D1 to D4, respectively.
[0033]
The variable attenuators 26-1 to 26-4 attenuate the output signal lights of the data modulators 24-1 to 24-4 at an attenuation rate according to the control signal from the control device 28. The control device 28 varies the attenuation rates of the attenuators 26-1 to 26-4 so as to carry the attribute information PR1 to PR4 of each channel ch1 to ch4, as will be described in detail later. In order to reproduce a clock having a frequency corresponding to the base rate B, the time average attenuation rates (DC components) of the attenuators 26-2 to 26-4 are controlled to the same value, and the attenuation rate of the attenuator 26-1 is reduced. Control is performed so as to be larger than the time average attenuation rate (DC component) of the other attenuators 26-2 to 26-4.
[0034]
Output signal lights from the attenuators 26-1 to 26-4 are input to the multiplexer 34 via the phase modulators 30-1 to 30-4 and the delay units 32-1 to 32-4. The delay units 32-1 to 32-4 are provided for arranging the signal lights of the respective channels ch1 to ch4 in different time slots, and in order to realize this, the delay of the delay units 32-1 to 32-4 is performed. The times τ1 to τ4 are adjusted. The delay time τ1 of the delay device 32-1 may be zero. That is, the delay device 32-1 can be omitted. The delay units 32-1 to 32-4 and the multiplexer 34 correspond to an OTDM multiplexer. The bit rate of the output signal light from the multiplexer 34 is 160 Gb / s. The output signal light of the multiplexer 34 propagates through the optical transmission line 12 and enters the optical receiver 14.
[0035]
As described above, the control device 28 varies the attenuation rates of the attenuators 26-1 to 26-4 so as to carry the attribute information PR1 to PR4 of each of the channels ch1 to ch4. More specifically, control device 28 attenuates attenuators 26-1 to 26-4 in accordance with a signal obtained by digitally modulating the amplitudes of sine waves of frequencies W1 to W4 unique to channels ch1 to ch4 with attribute information PR1 to PR4. Fluctuating rate. This is, so to speak, AC control of the attenuation rates of the attenuators 26-1 to 26-4. As digital modulation, FSK, PSK, DPSK or DQPSK can be used. The frequencies W1 to W4 are, for example, about 100 kHz to 10 MHz, which is sufficiently lower than the base rate (40 GHz) of the data D1 to D4. Since the data amount of the attribute information is generally small, such a rate is sufficient. Further, at such a rate, the transmission of the data D1 to D4 and the clock extraction of the base rate B of OTDM are not adversely affected.
[0036]
In this way, the attribute information PR1 to PR4 of each channel ch1 to ch4 can be transmitted while being superimposed on the data D1 to D4 without consuming the band for the data D1 to D4. The attribute information PR1 to PR4 are, for example, channel identification information, transfer information (or routing information), and network management information. The network management information includes a failure occurrence notification and the like.
[0037]
The control device 28 also controls the time-average attenuation rates (DC components) of the attenuators 26-2 to 26-4 to the same value so that the optical receiver 14 can reproduce a clock having a frequency corresponding to the base rate B. At the same time, control is performed so that the attenuation rate of the attenuator 26-1 is larger than the time average attenuation rate (DC component) of the other attenuators 26-2 to 26-4.
For example, the same offset is set for the attenuation rate of the attenuators 26-2 to 26-4, and an offset larger than the offset of the attenuators 26-2 to 26-4 is set for the attenuation rate of the attenuator 26-1. Set. By this DC control, the pulse amplitude of the output signal light from the attenuator 26-1 becomes smaller than the pulse amplitude of the output signal light from the attenuators 26-2 to 26-4.
[0038]
As described above, when a plurality of signal lights having the same bit rate B (for example, 40 Gb / s) are time-division multiplexed, if the pulse amplitude of one channel is made sufficiently different from the pulse amplitude of another channel, Fourier As can be easily understood by recalling the conversion, the spectrum of the OTDM signal light includes a tone component having a frequency corresponding to the bit rate B. By extracting this tone component, the optical receiver 14 can reproduce the clock corresponding to the base rate B. For example, only by increasing the attenuation rate of the attenuator 26-1 by 0.13 dB from the attenuation rates of the other attenuators 26-2 to 26-4, the 40 GHz clock is transmitted to the optical receiver 14 as described later. I was able to extract.
[0039]
This effect can be extended to clock extraction at an intermediate frequency between the base rate B and the bit rate B × n of the time-division multiplexed optical signal composed of n channels. For example, when time-division multiplexing is performed on n channels of the same base rate B, by attenuating the optical pulse amplitudes of a plurality of appropriate channels in the n channels at the same rate, the n-channel time division multiplexed optical signal A clock with a frequency B × k (where k is an integer from 2 to n−1) can be extracted.
[0040]
The OTDM optical signal transmitted through the optical transmission line 12 is input to the optical receiving device 14. The configuration and operation of the optical receiver 14 will be described. The OTDM optical signal propagated through the optical transmission line 12 is split into two by a demultiplexer 40, one of which is input to an optical amplifier (for example, an erbium-doped optical fiber amplifier (EDFA)) 42, and the other is a clock recovery device. Input to 44.
[0041]
The clock reproducing device 44 includes a photodetector 46 that converts the 160 Gb / s optical signal input to the optical transmission line 12 into an electric signal, an amplifier 48 that amplifies the output of the photodetector 46, and a clock synchronized with the output of the amplifier 48 to 40 GHz. (Phase Locked Loop) circuit 50 that extracts and generates the signal, an amplifier 52 that amplifies the output of the PLL circuit 50, a band-pass filter (BPF) 54 that extracts only the 40 GHz component from the output of the amplifier 52, and delays the output of the BPF 54 And a delay circuit 56 for timing adjustment. The configuration itself of the clock recovery device 44 is known for clock recovery. It is characteristic that a clock of 40 GHZ corresponding to the bit rate B of one channel is reproduced from the signal light of 160 Gb / s without adding a special circuit. This is possible because, as described above, the output of the light receiver 46 includes a tone component having a frequency corresponding to the base rate B of time division multiplexing. Therefore, the delay circuit 56 outputs a clock signal of 40 GHz.
[0042]
The 40 GHz clock signal output from the clock reproducing device 44 (delay circuit 56) is amplified by an amplifier 58 and applied as a drive signal to a mode-locked laser (MLLD) 60. As a result, the MLLD 60 oscillates a laser pulse at 40 GHz and outputs a control pulse light of 40 GHz.
[0043]
The control pulse light output from the MLLD 60 is input to a control terminal C of an optical separation device 66 via an optical amplifier (for example, an erbium-doped optical fiber amplifier (EDFA)) 62 and a phase adjuster 64. The output signal light of the optical amplifier 42 is input to the data input terminal D of the optical separation device 66. The optical separation device 66 converts the OTDM optical signal input to the data input terminal D into each of the channels ch1, ch2, ch3. The signal light is split into the signal light of ch4 and output from the output ports 1 to 4. The light separating device 66 is composed of, for example, a light-controlled optical switch. An optical switch that can be used for separating OTDM signal light is, for example, an I.O. Shakeet al. , "160 Gbit / s full OTDM demultiplexing based FWM of SOA-array integrated on planer lightwave circuit," Proc. 27th, European Conference on Optical Communication (ECOC'01), Tul. 2.2, pp. 182-183, 2001.
[0044]
The optical separation device 66 outputs the signal light of each of the channels ch1 to ch4 from separate output ports 1 to 4. If the transmission error on the optical transmission line 12 is neglected, the outputs of the respective channels ch1 to ch4 of the optical demultiplexer 66 correspond to the outputs of the attenuators 26-1 to 26-4. Attribute information PR1 to PR4 are multiplexed.
[0045]
With the configuration described above, there is no guarantee that the signal light of the channel ch1 is output from the output port 1 of the optical separation device 66. However, by controlling the phase adjuster 64 by the frequency discriminating circuit 82 and the phase control device 84 described later, it is possible to guarantee that the signal light of the channel ch1 is output from the output port 1 of the optical separation device 66. The details will be described later.
[0046]
Each of the demultiplexers 68-1 to 68-4 divides the output signal light of the corresponding channel of the optical demultiplexer 66 into two, outputs one as a payload signal of the corresponding channel, and outputs the other as an attribute demodulator 70-. 1 to 70-4.
[0047]
In the attribute demodulation device 70-1, the light receiver 72 converts the output signal light of the splitter 68-1 into an electric signal. The output of the light receiver 72 is amplified by the amplifier 74 and applied to the multiplier 76. The output of the multiplier 76 is applied to the control terminal of the local oscillator 80 via the loop filter 78. The local oscillator 80 oscillates at a frequency and a phase according to the output voltage of the loop filter 78. The output of the oscillator 80 is applied to a multiplier 76. The multiplier 76 multiplies the output of the amplifier 74 by the output of the oscillator 80.
The attribute information PR1 is demodulated by the square detection in the multiplier 76.
[0048]
When the signal light output from the output port 1 of the optical separation device 66 is the signal light of ch1, the oscillator 80 oscillates at the frequency W1. When the signal light output from the output port 1 of the optical separation device 66 is not the signal light of ch1, the oscillator 80 oscillates at a frequency other than the frequency W1. Therefore, by examining the oscillation frequency of the oscillator 80, it can be determined whether or not the signal light output from the output port 1 of the optical separation device 66 is the signal light of ch1.
[0049]
The frequency identification circuit 82 checks whether or not the frequency of the output signal of the oscillator 80 is equal to the frequency W1, and outputs a match signal to the phase control device 84 if they match, and outputs a mismatch signal if they do not match. When the frequency of the output signal of the oscillator 80 is not equal to the frequency W1, the phase control device 84 sweeps the amount of phase adjustment in the phase adjuster 64, and when the frequency identification circuit 82 outputs a coincidence signal, With the frequency of the output signal equal to the frequency W1, the phase adjustment amount of the phase adjuster 64 is fixed. As a result of this phase control, the signal light output from the output port 1 of the optical separation device 66 becomes the signal light of ch1.
[0050]
The separation order of the light separation device 66 is generally constant. That is, the signal light of ch2 is output from the output port 2 of the optical separation device 66, the signal light of ch3 is output from the output port 3, and the signal light of ch4 is output from the output port 4.
[0051]
By changing the frequency of comparison in the frequency identification circuit 82, the correspondence between each output port of the optical separation device 66 and the channel can be changed. For example, when the frequency to be compared in the frequency identification circuit 82 is changed to the frequency W2, the optical separation device 66 outputs the signal light of the channel ch2 from the output port 1 and outputs the signal light of the channel ch3 from the output port 2, The signal light of the channel ch4 is output from the output port 3, and the signal light of the channel ch1 is output from the output port 4.
[0052]
In the present embodiment, in the optical time division multiplexing transmission, by setting the optical pulse amplitude of one or a plurality of channels to a level different from the pulse amplitude of the remaining channels and transmitting the optical transmission path, the optical receiving apparatus has the following advantages. A clock having a frequency corresponding to the channel bit rate or an integral multiple thereof can be reproduced. This means that one of the clock synchronization signals having a plurality of discrete frequencies can be selectively transmitted.
[0053]
By modulating the pulse amplitude of each channel with a tone signal having a different frequency for each channel, the optical receiver can easily identify each channel.
[0054]
Further, by modulating the pulse amplitude of each channel with the attribute information of each channel, the attribute information of each channel can be transmitted without affecting the main data transmission and its band. At this time, by modulating the pulse amplitude of each channel with a tone signal having a different frequency for each channel, the optical receiver can easily identify the signal light of each channel after separating the OTDM signal light.
[0055]
【The invention's effect】
As can be easily understood from the above description, according to the present invention, a clock having a frequency corresponding to the base rate of the OTDM signal light or an integer multiple thereof can be transmitted. Further, the attribute information of each channel can be transmitted without affecting the main data transmission and its band. With these, a more efficient optical transmission system can be constructed.
[Brief description of the drawings]
FIG. 1 is a schematic block diagram of an embodiment of the present invention.
[Explanation of symbols]
10: Optical transmitter
12: Optical transmission line
14: Optical receiver
20: pulse light source
22: Optical splitter
24-1 to 24-4: Data modulator
26-1 to 26-4: Variable attenuator
28: Control device
30-1 to 30-4: Phase modulator
32-1 to 32-4: delay device
34: multiplexer
40: Demultiplexer
42: Optical amplifier
44: Clock recovery device
46: Receiver
48: Amplifier
50: PLL (Phase Lock Loop) Circuit
52: Amplifier
54: Bandpass filter (BPF)
56: Delay circuit
58: Amplifier
60: Mode-locked laser (MLLD)
62: Optical amplifier
74: phase adjuster
66: Light separation device
68-1 to 68-4: duplexer
70-1 to 70-4: Attribute Demodulator
72: Receiver
74: Amplifier
76: Multiplier
78: Loop filter
80: Local oscillator
82: Frequency identification circuit
84: Phase control device

Claims (21)

A system for transmitting a clock synchronization signal in an optical transmission system in which pulse signal light of n (integer) channels of a base rate (B) is time-division multiplexed and transmitted through an optical transmission line (12),
The pulse amplitudes of the signal light of k (k is 1 or more and less than n) channels out of the pulse signal lights of the n channels before the optical time division multiplexing are set to levels relatively different from the pulse amplitudes of the remaining channels. Amplitude adjustment devices (26-1 to 26-4, 28) for adjusting
A photoelectric converter (46) for converting the time-division multiplexed signal light transmitted through the optical transmission line (12) into an electric signal;
According to the output of the photoelectric converter (46), k frequencies whose frequency is equivalent to an integer multiple of the base rate (B) and whose level is adjusted by the amplitude adjusters (26-1 to 26-4, 28) A clock generation circuit (50) for generating a clock synchronization signal having a frequency determined by said channel. The clock synchronization signal transmission system according to claim 1, wherein k is 1. The amplitude adjusters (26-1 to 26-4, 28) include n variable level adjusters (26-1 to 26-4) capable of adjusting the level of signal light of each channel, and n variable level adjusters. The clock synchronization signal transmission system according to claim 1, further comprising a control device (28) for controlling the level adjusters (26-1 to 26-4). Pulse signal light generators (20, 22, 24-1 to 24-4) for generating pulse signal lights of n (integer) channels of a base rate (B) for carrying data;
The pulse amplitude of a predetermined one-channel pulse signal light among the n-channel pulse signal lights output from the pulse signal light generation device (20, 22, 24-1 to 24-4) is set to another pulse amplitude. An amplitude adjusting device (26-1 to 26-4, 28) for adjusting the pulse amplitude to a level relatively different from the pulse amplitude of the pulse signal;
Multiplexers (32-1 to 32-4, 34) for time-division multiplexing pulse signal light of each channel output from the amplitude adjusters (26-1 to 26-4, 28) and outputting OTDM signal light When,
An optical transmission line (12) for transmitting the OTDM signal light output from the multiplexing device, a duplexer (40) for dividing the OTDM signal light input from the optical transmission line (12) into two,
A clock regenerating device (44) for regenerating a clock synchronization signal having a frequency corresponding to the base rate (B) from one output signal light of the splitter (40), wherein one of the splitters (40) Photoelectric converter (46) that converts the output signal light into an electric signal, and a clock generation circuit that generates a clock synchronization signal having a frequency corresponding to the base rate (B) according to the output of the photoelectric converter (46). A clock recovery device (44) comprising (50);
It has a plurality of output ports and separates the other output signal light of the splitter (40) into signal light of each channel according to the clock synchronization signal recovered by the clock recovery device (44). A data transmission system comprising: an optical separation device (66) that outputs signal light from different output ports. The amplitude adjusters (26-1 to 26-4, 28) include n variable level adjusters (26-1 to 26-4) capable of adjusting the pulse amplitude of the pulse signal light of each channel, and the n The data transmission system according to claim 6, further comprising a control device (28) for controlling the number of variable level adjusters (26-1 to 26-4). The data transmission system according to claim 5, wherein the control device (28) changes a level adjustment amount of the n variable level adjusters (26-1 to 26-4) according to attribute information of each channel. 7. The device according to claim 6, further comprising a plurality of attribute demodulators (70-1 to 70-4) for demodulating the attribute information from the pulse signal light output from each output port of the optical separation device (66). Data transmission system. The data transmission system according to claim 7, wherein the attribute information includes at least one of channel identification information, transfer information, and network management information. Further, an identification device (82) for identifying whether or not the pulse signal light output from a predetermined output port of the optical separation device (64, 66) is the signal light of the predetermined channel; and an identification device (82). 5) a phase adjuster (64, 84) for adjusting the phase of a clock synchronization signal supplied from the clock recovery device (44) to the optical separation device (66) according to the identification result of (4). Data transmission system. The amplitude adjustment device (26-1 to 26-4, 28) includes n variable level adjusters (26-1 to 26-4) capable of adjusting the level of signal light of each channel, and attributes of each channel. The data transmission according to claim 9, further comprising a control device (28) that controls a level adjustment amount of the variable level adjusters (26-1 to 26-4) according to tone signals having different frequencies for each channel that carries information. system. The device according to claim 10, further comprising a plurality of attribute demodulators (70-1 to 70-4) for demodulating the attribute information from the pulse signal light output from each output port of the optical separation device (66). Data transmission system. The data transmission system according to claim 11, wherein the attribute information includes at least one of channel identification information, transfer information, and network management information. The pulse signal light generation device generates a pulse light source (20) that generates a light pulse having a frequency corresponding to the base rate (B), and a duplexer that divides output light of the pulse light source (20) into n channels ( The data transmission system according to claim 4, comprising: (22) and n data modulators (24-1 to 24-4) that modulate each output of the duplexer (22) according to transmission data. A method for transmitting a clock synchronization signal in an optical transmission system for transmitting an optical transmission line (12) by time-division multiplexing pulse signals of n (integer) channels of a base rate (B),
The pulse amplitude of k (k is 1 or more, less than n) of the signal light of the channel of the signal light of n channels is adjusted to a level relatively different from the pulse amplitude of the remaining channels, and Transmitting the optical transmission line (12),
Converting the time-division multiplexed signal light transmitted through the optical transmission line (12) into an electric signal;
According to the electric signal, the PLL circuit (50) generates a clock synchronization signal having a frequency corresponding to an integer multiple of the base rate (B) and having a frequency determined by the k channels whose amplitude has been adjusted before transmission. A clock synchronization signal transmission method. 15. The clock synchronization signal transmission method according to claim 14, wherein k is 1. A pulse signal light generator (20, 22, 24-1 to 24-4) generates pulse signal light of n (integer) channels of a base rate (B) for carrying data,
By the amplitude adjusting devices (26-1 to 26-4, 28), the pulse signal light of n channels output from the pulse signal light generating device (20, 22, 24-1 to 24-4) is output. Adjusting the pulse amplitude of the predetermined one-channel pulse signal light to a level relatively different from the pulse amplitudes of the other pulse signals;
The signal light of each channel output from the amplitude adjusters (26-1 to 26-4, 28) is time-division multiplexed, and the obtained OTDM signal light is output to the optical transmission line (12) to perform the optical transmission. The OTDM signal light input from the path (12) is split into two by a splitter (40),
One output signal light of the splitter (40) is converted into an electric signal, and a PLL circuit generates a clock synchronization signal having a frequency corresponding to the base rate (B) according to the electric signal,
A data transmission method characterized by separating the other output signal light of the demultiplexer (40) into signal light of each channel by an optical separation device (66) in accordance with the generated clock synchronization signal. When adjusting the pulse amplitude of a predetermined one-channel pulse signal light to a level relatively different from the pulse amplitude of another pulse signal, the pulse amplitude of the signal light of each channel is varied according to the attribute information of each channel. 17. The data transmission method according to claim 16, wherein: 18. The data transmission method according to claim 17, wherein the pulse amplitude of the signal light of each channel is varied according to a tone signal having a different frequency for each channel that carries attribute information of each channel. 19. The data transmission method according to claim 17, wherein the attribute information is demodulated from the pulse signal light output from each output port of the optical separation device (66). 19. The data transmission method according to claim 17, wherein the attribute information includes at least one of channel identification information, transfer information, and network management information. Further, it is determined whether or not the pulse signal light output from a predetermined output port of the light separation device (66) is the signal light of the predetermined channel, and the light separation device (66) is determined according to the identification result. 17. The data transmission method according to claim 16, wherein the phase of the supplied clock synchronization signal is adjusted.

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